A polycarbonate-based resin is a polymer excellent in transparency, heat resistance, and impact resistance and is widely used at present as an engineering plastic in the industrial field.
As a method of producing the polycarbonate-based resin, a method involving allowing an aromatic dihydroxy compound, such as bisphenol A, and phosgene to react directly with each other (interfacial polymerization method) is known as a method of producing a high-quality polycarbonate. As a method of industrially producing a polycarbonate by an interfacial polymerization method, there is adopted a method involving allowing phosgene and an alkaline aqueous solution of a bisphenol to react with each other in the presence of an organic solvent to produce a polycarbonate oligomer having a reactive chloroformate group, and simultaneously or sequentially with production of the polycarbonate oligomer, further subjecting the polycarbonate oligomer and the bisphenol to a polycondensation reaction in the presence of a polymerization catalyst, such as a tertiary amine, and an alkaline aqueous solution.
The organic solvent used in a reaction step and a washing step is typically purified by a method, such as distillation, after its recovery to be reused in the reaction step and the like (including a phosgenation reaction step, a polycondensation reaction step, and the washing step) (see Patent Document 1). In addition, waste water after the reaction step, waste water produced in the washing step, or waste water produced in a granulating step contains an inorganic matter such as sodium chloride, and an organic matter such as a phenol or a polycarbonate. In order to purify the waste water by removing the organic matter from an aqueous phase, an organic solvent is used to extract and remove the organic matter from the waste water. The organic solvent containing the phenol and the polymer that have been extracted and removed is reused in the polycondensation reaction step (see Patent Document 2).
Among the polycarbonate-based resins, a polycarbonate-polyorganosiloxane polymer (hereinafter sometimes referred to as “PC-POS”) has been attracting attention because of its high impact resistance, high chemical resistance, and high flame retardancy, and the polymer has been expected to find utilization in a wide variety of fields, such as the field of electrical and electronic equipment and the field of an automobile.
As a method of producing the PC-POS, there is known a method involving allowing a dihydric phenol-based compound and phosgene to react with each other to produce a polycarbonate oligomer, and polymerizing the polycarbonate oligomer with a polyorganosiloxane in the presence of methylene chloride, an alkaline compound aqueous solution, a dihydric phenol-based compound, and a polymerization catalyst (see Patent Document 3).